It is well known in the engine arts to control the firing and/or fuel injection timing of an internal combustion engine by use of a rotary signal encoder driven by the engine's crankshaft. Such an encoder typically employs a beam or field chopper such as a toothed wheel to generate an alternating signal indicative of the instantaneous rotational position and rotational speed of the crankshaft. A typical crank wheel chopper has 58 peripheral teeth comprising a 50% duty cycle (teeth and gaps of equal angular length). A timing gap equivalent to about three teeth is also included to permit the system to recognize the completion of each revolution and the start of the next revolution.
A problem in the prior art is that electrical noise in the engine, which may arise from any of a variety of sources, may interrupt and distort the true signal, either in the timing gap or between true teeth signals, producing signal spikes which are interpreted by the engine controller as valid. The controller then counts 59 (or more) teeth in a revolution, which cannot be computed by the prior art timing algorithm. This causes loss of synchronization of firing and/or fuel injection with the piston and valve sequencing, which can result in misfiring and incorrect spark and fuel delivery.
What is needed in the art is a system (method and apparatus) for recognizing and rejecting such spurious signals by continuing analysis of the true signal.
It is a principal object of the present invention to improve performance of an internal combustion engine by increasing the reliability of a crank encoder signal.